Method and machine for wrapping infusion bags in outer envelopes

ABSTRACT

A method and related machine for wrapping filter-bags ( 1 ) in sealed outer envelopes (S) comprises the following steps: feeding single, plane sheets ( 6 ) to a station ( 7 ) for wrapping each sheet ( 6 ) over a corresponding filter bag ( 1 ); folding the sheet ( 6 ) into a U-shape about a transversal axis (X) of the sheet ( 6 ) itself so as to form at least two opposite wings ( 6   a,    6   b ) between which the filter bag ( 1 ) is placed; rolling the longitudinal edges ( 8   a,    8   b ) of the U-shaped sheet ( 6 ) so as to flatten them; and, lastly, joining at least the longitudinal edges ( 8   a,    8   b ) of the U-shaped sheet ( 6 ) to form a sealed outer envelope (S) around the filter bag ( 1 ).

TECHNICAL FIELD

[0001] The present invention relates to a method for wrapping filterbags for products for infusion such as coffee, tea, camomile and thelike in sealed outer envelopes and the machine that implements themethod.

BACKGROUND ART

[0002] At present, machines for making filter bags comprise a pluralityof stations, located one after the other, in which the filter bags aremade. Each filter bag contains a charge of product closed in acorresponding chamber. Depending on the type of product it contains andthe machine used to make it, the filter bag has one or two chambers andis joined in one of several different known ways (for example, byknotting, heat sealing or by means of a heat sealed stamp) to a stringthat connects it to a pick-up tag which is joined in one of severaldifferent known ways (for example, by knotting, heat sealing or by meansof a stamp) to the free end of the string.

[0003] The string and the pick-up tag are suitably positioned on thefilter bag thus made (for example wound around the bag and connected toit or tucked inside it) to form a product that as ready to be packed insuitable cartons or boxes.

[0004] Before groups of filter bags are packed in boxes, the filter bagsmay be individually wrapped in an outer envelope consisting of a sheetof wrapping material folded around each filter bag and heat sealed inone or two different ways: on at least two longitudinal sides or edgesof the outer envelope if the latter has an opening flap folded over oneof the surfaces of the envelope itself; or simultaneous heat sealing onthree sides of the outer envelope, that is to say, two longitudinaledges and one transversal edge, if the envelope is of the simple type,that is to say, without the opening flap.

[0005] Known machines used to wrap the filter bags in individual outerenvelopes have a filter bag handling station comprising a plurality ofgrippers mounted radially on a starwheel, each being designed to pick upa single filter bag. As the starwheel turns, the filter bags are carriedto different stations where the string and tag are joined to each otherand to the filter bag and then to an wrapping station where a web ofwrapping material is cut into separate sheets, each of which will formthe outer envelope of a corresponding filter bag.

[0006] Close to this station, the filter bag is moved radially away fromthe starwheel to enable the sheet of wrapping material to be fed betweenit and the starwheel. The filter bag is then moved close to thestarwheel again to enable the sheet of wrapping material to be foldedinto a U shape around the filter bag. During this step, the opening flapof the outer envelope may also be formed by suitable folding means atthe station, the flap being held in place by a presser element on thegripper elements on the starwheel.

[0007] After this, the filter bag with the sheet of wrapping materialfolded in a U shape around it, is carried to a sealing station where twoor three edges of the sheet formed by the previous folding operation aresealed by suitable sealing means consisting of two or three elementsdepending on the type of outer envelope to be made.

[0008] The filter bag thus sealed in its outer envelope is then fed tothe stacking and final cartoning stations.

[0009] This method, consisting in sealing the edges of the outerenvelope after simply folding it, often results in a poor quality finishowing to the difficulty of correctly sealing the two longitudinal edgesand, in the case of a simple outer envelope without opening flap, thetransversal edge simultaneously. Indeed, during the folding step, thelongitudinal edges in particular, are difficult to place squarely overeach other since the wrapping material follows the shape of the filterbag which is not firm enough to enable a neat, square fold to be made.This results in skew seals and crinkling along the edges of the outerenvelope which are not only unattractive but which also do notadequately protect the product inside. This problem is accentuated bythe physical properties of the wrapping material from which the outerenvelope is made and whose relative rigidity prevents it from keepingits shape before and after sealing.

DISCLOSURE OF THE INVENTION

[0010] The present invention has for an object to overcome the abovementioned problem by providing a method and a machine for wrappingfilter bags in sealed outer envelopes in an extremely simple, fast andefficient manner without altering the general structure or existingmachinery for this purpose, so as to make outer envelopes of goodquality and ensuring a proper seal.

[0011] Accordingly, the invention provides a method for wrapping filterbags for products for infusion in individual sealed outer envelopes, thefilter bags being of the type comprising at least one chamber containinga charge of product and a string connected at one end to the chamberitself, while the other end of the string is connected to a pick-up tag,the method comprising the following steps: feeding a succession ofsingle, plane sheets to a station or wrapping each sheet over acorresponding filter bag; folding the sheet into a re-shape about atransversal axis of the sheet itself so as to form at least two oppositewings between which the filter bag is placed; and joining at least thelongitudinal edges of the U-shaped sheet to form a sealed outer envelopearound the filter bag; the method being characterised in that betweenthe step of folding the sheet and the step of joining its longitudinaledges, it comprises a further step of rolling the longitudinal edges soas to flatten them.

[0012] The present invention also provides a machine for wrapping filterbags for products for infusion in individual sealed envelopes, thefalter bags being of the type comprising at least one chamber containinga charge of product and a string connected at one end to the chamberitself, while the other end of the string is connected to a pick-up tag,the machine comprising handling means for moving each filter bag in aworking direction towards a station for wrapping a single, plane sheetof wrapping material around the filter bag; means for folding the sheetof wrapping material about a transversal axis of it to form a U-shapedwrapping around the filter bag, with at least two opposite wings betweenwhich the filter bag is placed; and a station for joining at least twolongitudinal edges of the U-shaped wrapping sheet to form a singlesealed envelope around the filter bag; the machine further comprisingbetween the wrapping station and the joining station a rolling stationdesigned to flatten the longitudinal edges.

[0013] The technical characteristics of the invention, in accordancewith the above-mentioned aims, are set out in the claims herein and theadvantages more clearly illustrated in the detailed description whichfollows, with reference to the accompanying drawings, which illustratepreferred embodiments of the invention without restricting the scope ofthe inventive concept, and in which:

[0014]FIGS. 1 and 2 are front and perspective views showing a wrappingfor a product for infusion with a sealed outer envelope, made using themethod according to the present invention and having a front flap foropening the envelope itself;

[0015]FIG. 3 is a front view of another wrapping for a product forinfusion, with an outer envelope made using the method according to thepresent invention and sealed on three of its edges;

[0016]FIG. 4 is a schematic perspective view, with some parts cut awayfor clarity, of a part of a machine for making filter bags and wrappingthem in individual sealed outer envelopes according to the presentinvention;

[0017]FIG. 5 is a partial perspective view of another embodiment of themachine illustrated in FIG. 4;

[0018]FIG. 6 is a schematic side view, with some parts cut away in orderto better illustrate others, of an operating station forming part of themachine shown in FIGS. 4 and 5;

[0019]FIG. 7 is a scaled-up schematic side view of a part of the machineillustrated in FIGS. 4, 5 and 6;

[0020]FIG. 8 is a schematic top plan view of a portion of a web ofwrapping material used to make outer envelopes for filter bags havingsome parts with cold glue on them.

[0021] With reference to the accompanying drawings, in particular FIGS.1 to 3, the method for wrapping filter bags in individual sealed outerenvelopes can be used for filter bags 1 comprising one or two chambers2, each containing a charge 3 of product and a string 4 connected at oneend to the chamber or chambers 2 and a tag 5 connected to the other endof the string 4 (a double chamber filter bag is illustrated purely byway of example in FIG. 2).

[0022] As shown in FIGS. 1 to 4, the filter bag 1 is wrapped in a sealedouter envelope S made from a sheet 6 of paper or heat-sealable wrappingmaterial or material having some parts with cold glue on them (asdescribed in more detail below), which is folded into a U shape.

[0023] In a first wrapping style (see FIGS. 1 and 2), the sealed outerenvelope S as made from a sheet 6 preferably of paper, folded into a Ushape to form two wings 6 a and 6 b, between which the filter bag 1 isplaced, and has an opening flap 9 formed by an extension of the wing 6 afolded over itself and over the other wing 6 b, and two longitudinaledges Sa and 8 b made by joining the corresponding longitudinal edges ofthe wings 6 a and 6 b of the sheet 6.

[0024] In a second wrapping style (see FIG. 3), the sealed outerenvelope S is made from a sheet 6 preferably of heat-sealable materialor of material having parts with cold glue on them, folded into a Ushape to form two wings 6 a and 6 b between which the filter bag 1 isplaced. This wrapping has a top end 10 made by joining, preferably byheat sealing or by simply pressing, the transversal edges or ends 10 aand 10 b of the corresponding wings 6 a and 6 b of the sheet 6, and twolongitudinal ends 8 a and 8 b made by joining, preferably by heatsealing or by simply pressing, the corresponding longitudinal edges orthe wings 6 a and 6 b.

[0025] The wrapping method, implemented by the machine M illustrated inFIG. 4 as described in more detail below, comprises the following steps:feeding a succession of single, plane sheets, cut off from a web ofwrapping material, to a station 7 for wrapping the sheets 6 around thefilter bags 1; at the station 7, folding each sheet 6 about atransversal axis X of the sheet 6 to form a U-shaped wrapping around acorresponding filter bag 1 with at least two wings 6 a and 6 b facingeach other; looking in more detail, the folding operation itself isperformed in a known manner by lowering the filter bag 1, placing thesheet 6 between the filter bag 1 and suitable handling means 12, andthen raising the filter bag 1 towards the means 12 (see arrows F3 and F4in FIGS. 4 and 5); rolling the longitudinal edges 8 a and 8 b of thewings 6 a and 6 b of each U-shaped wrapping together on both sides ofthe U-shaped wrapping so as to flatten the longitudinal edges 8 a and 8b and keep them aligned; joining the longitudinal edges 8 a and 8 b ofthe sheet 6 to a form a single, sealed outer envelope S containing afilter bag 1.

[0026] If sheets 6 with cold glue on the edges 8 a and 8 b and on thetransversal ends 10 a and 10 b (as shown in FIG. 8) are being used, therolling and joining steps are performed simultaneously since the rollingaction also has the effect of pressing together the parts with the coldglue on them.

[0027] If the sheet 6 folded into a U shape includes the opening flap 9(shown in FIGS. 1 and 2), previously formed according to a known method,which is not illustrated, during the step of folding the wings 6 a and 6b, the rolling step is also applied to the outer edges 9 a and 9 b ofthe open flap 9 itself, so as to correctly align the outer edges 9 a and9 b with the longitudinal edges 8 a and 8 b below them.

[0028] Instead, if the U-shaped sheet 6 is of the type illustrated inFIG. 3 to be joined preferably by heat sealing on three edges or sides,the method comprises a further step of joining the transversal edges 10a and 10 b preferably by heat sealing before the step of rolling thelongitudinal edges 8 a and 8 b of the wings 6 a and 6 b (see FIG. 5 inparticular)

[0029] In this case too, if the transversal edges 10 a and 10 b havecold glue on them, the joining step is performed by simply pressing theeoges 10 a and 10 b together.

[0030] The method described above is implemented by the machine Millustrated in FIG. 4. The specific part of the machine to which thepresent invention relates comprises handling means 12 for moving thefilter bag 1 in a working direction A towards a plurality of stationsfor simultaneously completing the formation of the filter bag 1 withstring 4 and pick-up tag 5.

[0031] In particular, as illustrated in FIG. 7, the handling means 12comprise a rotary drum 12 p equipped radially with a plurality ofgripper elements 12 p for picking up, handling and releasing theindividual filter bags 1 and designed to carry each filter bag 1 to thewrapping station 7. The station 7 is equipped with means (of known typeand therefore not illustrated) for folding the sheet 6 into a U shapeabout a transversal axis X of it, so as to form the two wings 6 a and 6b.

[0032] After the station 7, there is a station 11 for joining thesuperposed longitudinal edges 8 a and 8 b of the U-shaped sheet 6 toform a sealed outer envelope S.

[0033] As shown clearly in FIG. 4, between the wrapping station 7 andthe station 11 for joining the longitudinal edges 8 a and 8 b, there isa station 14 for rolling the longitudinal edges 8 a and 8 b in order toflatten them.

[0034] If the sheets 6 used have edges 8 a, 8 b and 10 a, 10 b with coldglue on them, the rolling station 14 also constitutes the station 11 forjoining the longitudinal edges 8 a and 8 b. In other words, the station11 is not used (that is, it is disabled or not fitted to the machine).

[0035] As illustrated in FIGS. 4, 5 and 6, the rolling station 14comprises roller means 15 for the simultaneous and bilateral rolling ofthe longitudinal edges 8 a and 8 b so as to align the longitudinal edges8 a and 8 b prior to being joined or to actually join them.

[0036] As shown in more detail in FIG. 7, If the sealed outer envelope Shas an opening flap 9, each gripper 12 p forming part of the handlingmeans 12 comprises a presser element 12 a which keeps the flap 9 in afixed position against the outer surface of the wing 6 b until it getsnear the rolling station 14.

[0037] Instead, if the outer envelope S is of the type sealed on threesides or edges, there is a station 16 for joining the top edges 10 a and10 b of the sheet 6 by heal sealing or by simply pressing them together.The station 16 is located, relative to the working direction A, afterthe wrapping station 7 and before the rolling station 14. The joiningstation 16 (see FIG. 5) comprises a gripper element 17 with heated jaws,in the event of heat sealed outer envelope, designed to heat seal thetop ends 10 a and 10 b of the sheet 6 which is folded into a U shape.

[0038] The rolling station 14, illustrated in more detail in FIG. 6,comprises two opposite pairs of rollers 18 and 19 (shown schematicallyalso in FIGS. 4 and 5) The roller pairs 18 and 19 are supported by abridge structure 20 forming a channel C to allow the sheet 6 folded intoa U shape to pass through in a radial direction of feed F away from thegrippers 12 p.

[0039] The roller pairs 18 and 19 are located on the sides of the bridgestructure 20 and the rollers of each pair are in tangential contact witheach other in such a way as to flatten the sheet 6 folded into a Ubetween them while feeding it to the station 11 where the longitudinaledges 8 a and 8 b are joined.

[0040] The joining station 11, which operates only if the edges 8 a and8 b are heat sealed, comprises a rotary drum 21, whose outer surface hasrecesses 22 formed in it to accommodate the single sheets 6 wrapped in aU around the filter bags 1 feeding in fron the rolling station 14, and apressure head 23 mounted radially relative to the drum 21 and cesignedto join the longitudinal edges 8 a and 8 b, each recess 22 being movedto a position facing the head 23 and the head 23 then being movedtowards and pressed against it (see arrows F1 in FIG. 6).

[0041] If the sealed outer envelope S is of the type illustrated inFIGS. 1 and 2, the pressure head 23 comprises a knurled presser element23 of known type designed to 3 minimize edges 8 a and 8 b by knurling,acting in conjunction with the recesses 22, which are also preferablyknurled.

[0042] Instead, if the sealed outer envelope S is of the typeillustrated in FIG. 3, the pressure head 23 comprises a heated element23 designed to join the edges 8 a and 8 b by heat sealing.

[0043] Close to the drum 21, there are means 24 designed to guide theU-shaped sheet 6 as it feeds out of the rolling station 14 so that thesheet 6 is accommodated securely in the recess 22 prior to the joiningoperation performed by the head 23, which is angularly spaced relativeto the guide means 24.

[0044] The guide means 24 comprise a frame 25 closed on at least threesides, located close to the drum 21 to delimit an area through which theU-shaped sheet 6 feeds out of the rolling station 14 and where a recess22 is already positioned.

[0045] In addition to the frame 25, the guide means 24 may comprise apresser element 26 fitted above the frame 25 to form a top closureoperated by suitable synchronised drive means 27 that move it between araised position where the element 26 is away from the recess 22 and alowered position where the element 26 is in contact with a singleU-shaped sheet 6 feeding out of the rolling station 14 so as to locateit in the recess 22.

[0046] The method and the related machine described above thereforeachieve the above mentioned aims by introducing a rolling station thatflattens the longitudinal edges of the sheet so as to align andcorrectly position the edges over each other before the step of heatsealing them.

[0047] The method provides sealed outer envelopes of high quality andwithout crinkled edges.

[0048] Also, the rolling station introduced does not increase thecomplexity of the machine M since it is simply placed between thestarwheel and an existing roller on the machine, ever. if it is now alsoused for sealing and not only to convey the sealed outer envelopes tofurther cartoning stations.

[0049] Furthermore, it should be stressed that the rollers also act asfeed means between the starwheel and the longitudinal sealing roller,which means that the rolling station has a twofold function.

[0050] Moreover, if the sheets 6 being used are or the type with coldglue on them, the rolling station also functions as the sealing stationwhere the edges can be joined by simply pressing them together, thussimplifying the structure of the machine.

[0051] The use of rollers to flatten the edges of the outer envelopeimproves the quality of the end product because even if the materialused is relatively rigid, the edges remain properly in place until theyreach the point where the final seal is made.

[0052] The invention described can be subject to modifications andvariations without thereby departing from the scope of the inventiveconcept. Moreover, all the details of the invention may be substitutedby technically equivalent elements.

1. A method for wrapping filter bags (1) for products for infusion inindividual sealed outer envelopes (S), the filter bags (1) being of thetype comprising at least one chamber (2) containing a charge (3) ofproduct, and a string (4) connected at one end to the chamber (2)itself, while the other end of the string (4) is connected to a pick-uptag (5), the method comprising the following steps: feeding a successionof single, plane sheets (6) to a station (7) for wrapping each sheet (6)over a corresponding filter bag (1); folding the sheet (6) into aU-shape about a transversal axis (X) of the sheet itself around thefilter bag (1) so as to form at least two opposite wings (6 a, 6 b)between which the filter bag (1) is placed; and joining at least thelongitudinal edges (8 a, 8 b) of the sheet (6) folded into a U shape toform a sealed outer envelope (S) around the filter bag (1); the methodbeing characterised in that after the step of folding the sheet (6) itfurther comprises at least a step of rolling the longitudinal edges (8a, 8 b) so as to flatten them.
 2. The method according to claim 1,characterised in that the step of rolling the longitudinal edges (8 a, 8b) is performed between the step of folding the sheet (6) and the stepof joining the longitudinal edges (8 a, 8 b).
 3. The method according toclaim 1, where each sheet (6) has parts (8 a, 8 b) with cold glue onthem, characterised in that the step of rolling the longitudinal edges(8 a, 8 b) also constitutes the step of joining the longitudinal edges(8 a, 8 b) which are the parts with the cold glue on them.
 4. The methodaccording to claim 1, characterised in that the step of rolling thelongitudinal edges (5 a, 5 b) is performed simultaneously on bothlongitudinal edges (8 a, 8 b) and in such a way as to align the edges (8a, 8 b) with each other.
 5. The method according to claims 1 and 2,characterised in that the sheet (6) folded into a U shape also has on itan opening flap (9), extending from one of -he wings (6 a, 6 b) andformed by folding a portion of the wing (6 a) over itself in such a waythat its inner surface comes into contact with the outer surface of theother wing (6 b); the rolling step being performed also on thelongitudinal outer edges (9 a, 9 b) of the opening flap (9) so as toalso align them with the underlying longitudinal edges (8 a, 8 b) of theU-shaped sheet (6).
 6. The method according to claims 1 and 3, whereeach sheet (6) has parts (8 a, 8 b; 9 a, 9 b) with cold glue on them,characterised in that the sheet (6) folded into a U shape also has on itan opening flap (9), extending from one of the wings (6 a, 6 b) andformed by folding a portion of the wing (6 a) over itself in such a waythat its inner surface comes into contact with the outer surface of theother wing (6 b); the ro ling step being performed also on thelongitudinal outer edges (9 a, 9 b) of the opening flap (9) with coldglue on them so as to also align them with and join them to theunderlying longitudinal edges (8 a, 8 b) of the U-shaped sheet (6). 7.The method according to claim 1, characterised in that the step ofjoining the longitudinal edges (8 a, 8 b) is performed after the roilingstep which precedes a further step of joining too transversal edges (10a, 10 b) of the wings (6 a, 6 b) or the U-shaped sheet (6).
 8. Themethod according to claim 7, characterised in that the joins areeffected by heat sealing.
 9. The method according to c aim 7, where eachsheet (6) has parts (8 a, 8 b; 9 a, 9 b; 9 a, 10 b) with cold glue onthem, characterised in that the joins are effected by pressing.
 10. Themethod according to claim 2 or 4, characterised in that the rolling stepis performed while the sheet (6) which is folded into a U shape aroundthe filter bag (1) is being fed to a station (11) where the longitudinaledges (8 a, 8 b) are joined.
 11. A machine (M) for wrapping filter bags(1) for products for infusion in individual sealed envelopes (S), thefilter bags (1) being of the type comprising at least one chamber (2)containing a charge (3) of product and a string (4) connected at one endto the chamber (2) itself, while the other end of the string (4) isconnected to a pick-up tag (5), the machine comprising handling means(12) for moving each filter bag (1) in a working direction (A) towards astation (7) for wrapping a single, plane sheet (6) of wrapping materialaround the filter bag (1); means (13) for folding the sheet (6) ofwrapping material about a transversal axis (X) of it to form a U-shapedwrapping around the filter bag (1), with at least two opposite wings (6a, 6 b) between which the filter bag (1) is placed; and a station (11)for joining at least two longitudinal edges (8 a, 8 b) of the U-shapedwrapping sheet (6) to form a single sealed envelope (S) around thefilter bag (1); the machine (M) being characterised in that It furthercomprises, after the wrapping station (7), at least a rolling station(14) designed to flatten and join the longitudinal edges (8 a, 8 b). 12.The machine according to claim 11, characterised in that the station(14) for rolling the longitudinal edges (8 a, 8 b) is located betweenthe wrapping station (7) and the joining station (11).
 13. The machineaccording to claim 11, where each sheet (6) has parts (8 a, 8 b) withcold glue on them, cnaracterised in that the station (14) for rollingthe longitudinal edges (8 a, 8 b) also constitutes the Joining station(11) since it presses together the edges (8 a, 8 b) with the cold glueon them: so as to join them.
 14. The machine according to claim 11,characterised in that the rolling station (14) comprises roller means15) for simultaneously rolling the longitudinal edges (8 a, 8 b) anddesigned to align the longitudinal edges (8 a, 8 b) with each other. 15.The machine according to claim 11, characterised in that it furthercomprises means for forming from one of the wings (6 a, 6 b) on theU-shaped sheet (6) a flap (9) by folding a portion of the wing (6 a)over itself in such a way that its inner surface comes into contact withthe outer surface of the other wing (6 b); the filter bag (1) handlingmeans (12) comprising a presser element (12 a) which keeps the flap (9)in a fixed position against the outer surface of the wing (6 b) at leastuntil it gets near the rolling station (14).
 16. The machine accordingto claim 11, characterised in that between the wrapping station (7) andthe rolling station (14) there is a further station (16) for joining thetop transversal edges or ends (10 a, 10 b) of the U-shaped sheet (6).17. The machine according to claim 16, characterised in that the furtherjoining station (16) comprises a heated gripper element (17) designed toheat seal the top transversal edges or ends (10 a, 10 b) of the U-shapedsheet (6).
 18. The machine according to claim 16, where each sheet (6)nas parts (8 a, 8 b; 10 a, 10 b) with cold glue on them, characterisedin that the further joining station (16) comprises a gripper element(17) designed to press together the top transversal edges or ends (10 a,10 b) of the U-shaped sheet (6) which have cold glue on them.
 19. Themachine according to claim 11, characterised in that the rolling station(14) comprises two opposite pairs of rollers (18, 19), supported by abridge structure (20) forming a channel (C) to allow the sheet (6)folded into a U shape to pass through in a radial direction of feed (F)away from the handling means (12); the roller pairs (18, 19) beinglocated at the ends of the channel (C) and the rollers of each parr (18,19) being in tangential contact with each other in such a way as coflatten the sheet (6) folded into a U between them while at the sametime feeding it forward.
 20. The machine according to claims 11 and 12,characterised in that the station (11) for joining the longitudinaledges (8 a, 8 b) comprises a rotary drum (21), whose outer surface hasrecesses (22) formed in it to accommodate the single sheets (6) wrappedin a U around the filter bags (1) feeding in from the rolling station(14), and a pressure head (23) mounted radially relative to the drum(21) and designed to join the longitudinal edges (8 a 8 b), each recess(22) being moved to a position facing the head (23) and the latter thenbeing moved towards and pressed against it.
 21. The machine according toclaim 20, characterised in that the pressure head (23) comprises aheated element (23) designed to join the edges (8 a, 8 b) by heatsealing.
 22. The machine according to claim 20 or 21, characterised inthat the drum (21) is acted upon by means (24) designed to guide theU-shaped sheet (6) as it feeds out of the rolling station (14) so thatthe sheet (6) is accommodated securely in the recess (22) prior to thejoining operation performed by the head (23), which is angularly spacedrelative to the guide means (24).
 23. The machine according to claim 22,characterised in that the gu de means (24) comprise a frame (25) closedon at least three sides, located close to the drum (21) to delimit anarea through which the U-shaped sheet (6) feeds out of the rollingstation (14), such. area also comprising a recess (22).
 24. The machineaccording to claim 23, characterised in that the guide means (24)further comprise a presser element (26) frtted above the frame (25) toform a top closure operated by suitable synchronised drive means (27)that move it between a raised position where the element (26) is awayfrom the recess (22) and a lowered position where the element (26) is incontact with a single U-shaped sheet 16 feeding out of the rollingstation (14) so as to locate it in the recess (22).